1. Field of the Invention
The present invention relates to an automatic control apparatus, especially having saturation characteristics.
2. Description of the Prior Art
In general, it is known that the stability and the rapidity of response in the operation of automatic control apparatus are incompatible requirements which are difficult to fulfill simultaneously and are in such a contradictory relationship that, if the stability is improved, the response characteristic will deteriorate and vice versa.
It has been proposed in the past to change over the gains and/or time constants of an elastic or damping feedback element of the control apparatus in compliance with the quantity of operation of a controlled device such as the position of a servomotor or the like, for example. This method is disadvantageous in that the stability in the control operation is degraded in dependence upon the controlled quantity such as the positioning. According to another known method, saturation is imposed on the output of the damping feedback element both for the opening and the closing operations. This method certainly assures stability for such small or slow variations in the controlled quantity at which the damping feedback circuit may not be saturated. However, for a relatively large variation, satisfactory stability cannot be attained, because the damping feedback circuit is saturated for both the opening and the closing operations of the controlled device.